The present invention relates chiefly to a small bearing and, particularly, to a radial/thrust composite-bearing jointly having both functions of a slide bearing and a roller bearing.
Generally, a radial/thrust composite bearing of a roller bearing comprises, as a mechanism for receiving a radial load, an inner race (inner tube) and an outer race (outer tube), in which balls perform rolling motion between thrust plates. As a typical example thereof, there are shown in the attached drawings of FIGS. 8 and 9 a ball bearing type and a needle roller type, respectively.
On the other hand, in a slide bearing, a bearing surface receiving a thrust load and a bearing surface receiving a radial load perform relative sliding motion between these bearing surfaces and a shaft. FIG. 10 shows, as an example, a radial/thrust composite-type slide bearing having a bush configuration.
Conventionally, in a radial/thrust composite bearing of a roller bearing, there are many cases where a thrust plate 01 and a retainer 02 for retaining balls or rollers are arranged as separate parts, and are not integrated with a bearing body. For this reason, there are many inconveniences on assembling the bearing to a housing and on custody. Further, in case where the bearing is brought to a bearing of integrated type, the number of parts increases and, as a result, the bearing is brought to an expensive one.
Generally, the roller bearing is characterized in that the balls perform rolling motion between the inner ring and the outer ring. Also in the needle roller bearing, needle rollers perform rolling motion between the inner and outer rings or between the outer ring and the shaft.
Similarly, the radial/thrust composite rolling bearing is brought to a mechanism which receives a load by rolling contact while the balls or the needle rollers perform rotational movement and revolution. Furthermore, in case of the thrust load, transferring of the load is performed by rolling contact between the balls or the rollers. For this reason, for the outer tube, the inner tube, the thrust plate, the rollers and the needle roller, processing of quenching and polishing is required after machinery processing of the parts has been performed. Many steps and skillful technique are required and this increases the cost. Moreover, since heavy-load type and light-load type are the same in structure as each other, it is difficult to design a bearing thickness (t.sub.1) and a flange thickness (t.sub.2) thin like the slide bearing. For this reason, the radial/thrust bearing has a disadvantage that a bearing weight is excessive.
On the other hand, in the radial/thrust composite bearing of slide bearing type, it is required for the shaft to have a surface receiving the thrust load, and a high finishing precision and high hardness are required for the thrust surface of the shaft because the shaft and the bearing surface relatively slide with respect to each other. For this reason, there is a disadvantage that the cost for manufacturing the shaft increases.
Further, in a slide bearing having a small diameter, a radial/thrust composite bearing is light in weight and small in size as compared with a needle roller-type bearing. However, when the radial/thrust composite bearing is used under middle and high rotation (at not slower than 30 to 100 m/min of peripheral speed of bearing), oil supply is required, and there are problems in secureness of oil, oil discharge and the like. Furthermore, at locations where the bearing is used under no-lubrication, friction increases as compared with the rolling bearing. Thus, the radial/thrust composite bearing has such a disadvantage that a driving force for instruments increases.